Method and composition of matter for coating and coloring metal articles



Patented Aug. 6, 1929.

"UNITED STATES 1,723,051 PATENT OFFICE.

ALADAR IPAGZ, OF EAST CLEVELAND, OHIO.

METHOD AND COMPOSITION OF MATTER FOR COATING AND COLORING METAL ARTICLES.

no 'mawin g.

This invention relates to the coatin and coloring of metallic articles made who ly or chiefly of iron, steel, tin, aluminum, lead and magnesium, either alone or in admixture w1th each other or alloyed with smaller amounts of other metals. It has long been known that the metals cadmium and zinc when simply immersed in a solution of a soluble molybdate receive an adherent coating, but such procedure applied to any other metal has produced, either no result, or a pulverulent, nonadherent deposit unless by the use of an electrical potential, which may be produced either by contact with a suitable metal in the solution or by connection to an outslde source of electric energy. The objects of my present 1 invention are the provision of a simple, in-

expensive, rapid, and technically convenient process whereby a dense adherent and protective coating can be produced on common metals by the use of molybdenum compounds and without the necessity of electric potentials, and by the employment of manipulations so simple and safe that casual factory employes can perform the same.

I have discovered that this object can be attained by employing in connection with the molybdate solution, certain other substances either alone or in combination with each other as will hereafter be described.

The molybdates used are those of the alkali metals, namely sodium, potassium, lithium, or ammonium. It makes no difference which base is employed. Convenience and cheapness are the only considerations. The modifying or controlling salts which I prefer are classified as follows:

1. Salts of oxalic a0z'0l.-These are preferably the alkali salts of this radical, although with care the acid itself can be used and forms with the base already in the bath an oxalate. The molybdate is employed in strengths of from one-tenth of' one percent to one percent and the oxalate from, say, one-half percent toone. percent although I do not restrict myself to these exact proportions. However, it is best to use dilute solutions partly because the resulting coating is harder and denser and because there is less wastage by the rinsing process. In general it is best that the percentage of the oxalatebe at least as high as that of the molybdate.

2. Soluble fluoridea-These are preferably duced by sodium silico fluoride Application filed April 16, 1926. Serial No. 102,561.

used in the form of double fluorides, e. g. the double fluoride of some alkali metal such as sod1um with silicon, iron, aluminum, zircomum, tltanium, etc. In some cases a single fluoride alone (e. g. sodium fluoride) serves acceptably, but in general I find that a mixture of a single fluoride and a double fluoride serves every purpose in a cheap and reliable manner with the exception of treating lead articles. I find fluosilicates the cheapest and most economical, and this substance alone is entirely successful when used with the molybdate solution for articles made from or containing aluminum or tin. In the case of tin the single fluoride such as, sodium fluoride will likewise accomplish the desired result J when used with the molybdate solution as described, although sodium fluoride is a more expensive compound. Sodium fluoride also produces a very hard adherent coating when used with soluble molybdates for ferrous metal .articles although its action is slow. With ferrous metal articles'the coating proalone is not satisfactorily adherent but can be rendered so by the addition of sodium fluoride or, (what is essentially the same thing) by the addition of an alkali carbonate which reacts with the sodium silico fluoride to form some single fluoride. Accordingly, for convenient practical purposes, I prefer to employ a mixture of sodium silico fluoride, and a second alkali compound capable of reacting with such double fluoride which, in conjunction with the molybdate solution, forms a successful coating solution for the common metals I have mentioned. A very successful, cheap and reliable solution contains (per liter of water) 2 grams of sodium silico fluoride,

2 grams alkali carbonate,

2 grams of soluble molybdate; although I do not limit myself to these proportions;

3. Increased acidity.For example the addition of molydic acid, t-ungstic acid or boracic acid, produces with the soluble molybdate an acid salt and this produces for some reason a better adherence than is obtained by the neutral salt. I do not consider it as satisfactory as either the oxalate or the double fluoride but commercially successful results can be obtained. I have had successful results with an amount of these acids equ valent to one-tenth to one-fourth that of the soluble molybdate present.

4. Aluminum chloride-This is advantageous chiefly in connection with articles made of lead or its alloys. It gives noticeable results with ferrous metal articles,

' though I do not advocate it. However, as regards lead it affords better results apparently than any other substance even the oxalates. An example of a successful treating solution employing this ingredient is one containing 1 gram soluble molybdate; 5 grams aluminum chloride, one liter water. This solution yields the entire range of colors with leaden articles from blue, through yellow, red, green, brown to black. Theoxalates often serve to carry the coating. only to the red stage. Certain other salts can be used with leaden articles, e. gtaluminum sulphate, alums, magnesium salts, and manganese salts (such as the sulphate or chloride) but most of these yield only half the full range of colors.

5. Soluble polysz'licates.These appear to be successful only with ferrous metal articles. Such polysilicates are produced by adding an excess of silica to sodium silicate solution. A successful treating bath containing the same is made from soluble molybdate 2 grams; polysilicate gram, water 1 liter.

In each case the solution is preferably employed hot and the article to be treated is first thoroughly cleansed and immersed therein for from one-half minute to five minutes, more or less, dependent upon the depth and thickness of coating desired. There is no injuryfrom over immersion since the process I is self-arresting. The nature of preliminary acid or its soluble compounds prevents the treatment must be such as does not interfere with the operation of the bath. For example pickling the ferrous metal article in chromic successful performance of my coating process. On the other hand, although my process will not serve for the coating of copper articles,yet an advance treatment of a ferrous metal article by immersion in a copper containing solution so as to produce a flash coating of copper thereon results in a substantially improved deposit in the molybdenum 'like subsequent coatings.

The protective effect of this coating as applied to ferrous metal articles can also be enhanced by subsequent chemical treatment. I have discovered that despite the impossitreatment in a solution of chromic acid or its compounds, if the article after being coated be treated for a short time, c. g. five to ten minutes, in a solution of a soluble chromate (e. g. potassium or sodium chromate or bichromate), its resistance to wet or atmospheric corrosion is very greatly enhanced. I have had excellent results by boiling the articles for the length of time indicated in 5% chromate solution. I have had the best success of all in this rust-proofing process by first, pickling the ferrous metal article in a suitable bath such as sulphuric acid; second, producing a flash coating of copper thereon in a solution of copper sulphate; third, rinsing the copper solution from the article; fourth, immersing for from one-half minute to five minutes in a bath containing molybdenum and one of the other modifying ingredients heretoforedescribed; and, fifth, boiling in a solution of a soluble chromate salt. Malleable cast iron responds particularly well to thi procedure.

Of course I do not restrict myself to following the entire series of steps, since the immersion of the articles in the molybdate solution modified by a suitable energizing or activating reagent constitutes the essence of my invention and -the addition of the other steps or modifications in the reagent are regarded as colorable changes only. The employment of soluble oxalates as energizing or activating agents has been specifically claimed by' my copending application filed March 23, 1925, SerialNo. 17,799.

Having thus described my invention what I claim is:

1. The process of producing an adherent protective coating on ferrous metal articles which contains the steps of first producing a flash coating of copper thereon and afterward subjecting the articles to the action of a solution containing soluble salts of molybcontaining soluble salts of molybdenum and L 4. A dipping solution for producing an adherent colored coating on metal articles containing a soluble molybdate and a soluble salt of one Or more of the acids, oxalic, polysilicic, hydrofluoric, hydrofluosilicic.

5. A dipping solution for producing an adherent colored coating on metal articles 5 containing a soluble molybdate and a soluble fluorine com. ound.

6. A dipping solution forproducing an adherent colored coating on metal articles containing a soluble molybdate and a soluble double fluoride. 3

7. A dipping solution for the purpose described containing a soluble molybdate and sodium silico fluoride.

In testimony whereof I hereunto afiix my signature.

v ALADAR PACZ. 

